[systemd-devel] [User question] Unclear journal messages from systemd-resolved

Thu May 2 09:03:41 UTC 2024

Hi, I hope it’s OK to ask a question here (the About section said as much).

I’m receiving messages in the journal that I have difficulty 
interpreting. It appears to repeatedly switch from TCP to UDP and back, 
claiming that both are a “degraded feature set”…

Here is a sample journal output:
~$ journalctl --unit systemd-resolved.service -r | head -n 60
May 02 10:29:56 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:29:56 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:29:46 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:29:46 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:29:46 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:29:46 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:29:46 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:29:46 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:27:50 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:27:50 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:27:33 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:27:33 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:27:19 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:27:19 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:27:16 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:27:16 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:26:53 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:26:53 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:26:39 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:26:39 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:26:38 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:26:38 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:26:36 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:26:36 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:25:25 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:25:25 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:25:24 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:25:24 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:25:24 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:25:24 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:25:24 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:25:24 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:25:23 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:25:23 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:25:23 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:25:23 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:25:23 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:25:23 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:25:23 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:25:23 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:25:22 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:25:22 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:24:55 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:24:55 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:24:51 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:24:51 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:24:51 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:24:51 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:24:48 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:24:48 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:24:48 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:24:35 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of UDP+EDNS0 for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:24:35 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of UDP+EDNS0 for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:23:54 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:23:54 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:23:54 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:23:54 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:23:54 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.1.1.1#cloudflare-dns.com.
May 02 10:22:56 nailbox systemd-resolved[95890]: Using degraded feature 
set TCP instead of UDP for DNS server 1.0.0.1#cloudflare-dns.com.
May 02 10:22:56 nailbox systemd-resolved[95890]: Using degraded feature 
set UDP instead of TCP for DNS server 1.0.0.1#cloudflare-dns.com.

Do you know if this is intended behavior? What am I supposed to make of 
this?

Here is my /etc/systemd/resolved.conf:
[Resolve]
DNS=1.1.1.1#cloudflare-dns.com 1.0.0.1#cloudflare-dns.com 
2606:4700:4700::1111#cloudflare-dns.com 
2606:4700:4700::1001#cloudflare-dns.com

LLMNR=true
DNSSEC=false
DNSOverTLS=false

Here is the output of resolvectl status (with the local DNS redacted):
Global
            Protocols: +LLMNR +mDNS -DNSOverTLS DNSSEC=no/unsupported
     resolv.conf mode: stub
   Current DNS Server: 1.1.1.1#cloudflare-dns.com
          DNS Servers: 1.1.1.1#cloudflare-dns.com 
1.0.0.1#cloudflare-dns.com 2606:4700:4700::1111#cloudflare-dns.com 
2606:4700:4700::1001#cloudflare-dns.com
Fallback DNS Servers: 1.1.1.1#cloudflare-dns.com 8.8.8.8#dns.google 
1.0.0.1#cloudflare-dns.com 8.8.4.4#dns.google 
2606:4700:4700::1111#cloudflare-dns.com 2001:4860:4860::8888#dns.google
                       2606:4700:4700::1001#cloudflare-dns.com 
2001:4860:4860::8844#dns.google

Link 2 (docker0)
     Current Scopes: none
          Protocols: -DefaultRoute +LLMNR +mDNS -DNSOverTLS 
DNSSEC=no/unsupported

Link 3 (wlp4s0)
     Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6 mDNS/IPv4 mDNS/IPv6
          Protocols: +DefaultRoute +LLMNR +mDNS -DNSOverTLS 
DNSSEC=no/unsupported
Current DNS Server: ███████████████
        DNS Servers: ███████████████
         DNS Domain: intern

I’m using NixOS (24.05.20240425.7bb2ccd (Uakari)) and running systemd 
255.4. Here is the output of systemctl --version:
systemd 255 (255.4)
+PAM +AUDIT -SELINUX +APPARMOR +IMA +SMACK +SECCOMP +GCRYPT -GNUTLS 
+OPENSSL +ACL +BLKID +CURL +ELFUTILS +FIDO2 +IDN2 -IDN +IPTC +KMOD 
+LIBCRYPTSETUP +LIBFDISK +PCRE2 +PWQUALITY +P11KIT +QRENCODE +TPM2 
+BZIP2 +LZ4 +XZ +ZLIB +ZSTD +BPF_FRAMEWORK -XKBCOMMON +UTMP -SYSVINIT 
default-hierarchy=unified

Normally I have an Autocrypt header with PGP information but I just set 
up this system and haven’t configured GPG/Thunderbird with that yet.
Sincerely, Anselm Schüler (email <mailto:mail at anselmschueler.com>, 
website <https://anselmschueler.com/>)
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